The present invention relates to an instrument for the anterior correction of such conditions as scoliosis, in which there is twisting or bending of the vertebrae of the patient.
For example, the spine of a scoliosis patient exhibits bending into a bow shape by virtue of 3-dimensional twisting, and to correct the twisting and bending of the patient's vertebrae, it is necessary to correct not only the front-to-back curvature but the left-to-right curvature of the vertebrae making up the patient's spine.
Surgical means of treatment to correct vertebral twisting and bending in a scoliosis patient include the anterior correction method in which correction of the vertebrae is performed from the side (or, in medical terms, from the anterior), and the posterior correction method in which correction of the vertebrae is performed from the rear. The method of correcting twisting and bending of vertebrae of a scoliosis patient is applied not only to the usual scoliosis patients, but also in the treatment of damaged or chipped vertebrae or laterally slipped vertebrae caused by either accidents or tumors. Treatment in the case of scoliosis involves a large number of vertebrae to be treated, the treatment being applied across a large number of vertebrae.
A known treatment instrument used to perform anterior correction for the purpose of treatment in the case of damaged vertebrae or in the case of tumors will be described later in detail. This known treatment instrument comprises a pair of vertebra plates having spikes, vertebra screws which are screwed into the vertebrae through two holes provided in the top plate of each vertebra plate, two screw rods which link the vertebra screws in a pair, and holding nuts which fix the screw rods to the vertebra screw, the vertebra screws being formed by a head part, which has a rod hole, and a threaded shank, which is formed integral with the head part.
The mounting of the above treatment instrument to the patient is done by positioning the pair of vertebra plates with the spikes on the sides of the normal vertebrae before and after a vertebra which is damaged or chipped, and screwing the vertebra screws into each of the normal vertebrae through the two holes provided in the vertebra plate top plates. The vertebra plates are positioned by passing the screw rods through the holes provided in the heads of the vertebra screws which are screwed into the two normal vertebrae adjoining the damaged or chipped vertebra, and by adjusting the holding nuts to hold the screw rods to the heads of the vertebra screws. In doing this, because the screw rod is highly rigid and is in the form of a straight line, the insertion of the screw rods into the rod holes provided in the heads of the vertebra screws can only be done if the rod holes provided in the heads of the vertebra screws are aligned along one and the same straight line. Once the treatment instrument is mounted to the patient, the damaged or chipped vertebra or intervertebral disc is removed, a different bone or ceramic bone being inserted in that location to treat a patient with a damaged or chipped vertebra caused by an accident or a tumor.
In the above-noted treatment instrument, to link the two normal vertebrae adjoining a damaged or chipped vertebra, screw rods are passed through rod holes in the heads of vertebra screws of the normal vertebrae. The screw rods are highly rigid and in the form of a straight line, so that if the two normal vertebrae are positioned along a straight line, the hole in one vertebra screw provided in one normal vertebra will be along the same straight line as the hole in the other vertebra screw provided in the other normal vertebra. Therefore, there will be no interference with the task of passing the screw rod through the rod hole in the vertebra screw provided at one normal vertebra and then through the rod hole in the vertebra provided at the other normal vertebra.
However, it is normal for the vertebrae of a scoliosis patient to be twisted and bent, and located along a curved line, so that the vertebra screws provided at the vertebrae which exhibit front-to-back curvature and lateral curvature are located along a curved line, rather than a straight line. Therefore, the rod holes provided in the heads of the vertebra screws provided at the vertebrae are located along a curved line, making it impossible to perform the task of passing the highly rigid linear screw rod through the holes in the heads of the vertebra screws. Also, to hold the screw rods to the vertebra screws, it is necessary to adjust two holding nuts while screwing them onto each vertebra screw, making this task a troublesome and time-consuming and impractical one to perform in an operating room.